1. Field of the Invention
The invention relates to a method for converting carbon-containing raw material, particularly coal, wood or crude oil, into a combustible product gas by a gasification reaction with steam in the presence of a catalyst, which is dissolved in the steam intended for the gasification reaction, forming a gaseous homogeneous solution.
2. Description of the Prior Art
A method of this type is described in German Offenlegungsschrift No. 28 17 835 (Canadian Patent No. 11 24 521). According to this known method, steam in which the catalyst is homogeneously dissolved as a gas for improving the effectiveness the steam, is fed to a reaction vessel containing powdered coal or powdered coke. The reaction pressure in the reaction vessel is approximately in the range of 60 bar to 140 bar, while the reaction temperature is about 800.degree. C. to 850.degree. C. Alkali chlorides and alkali carbonates are used as the catalyst.
In the reaction vessel, gasification of carbon into carbon monoxide and hydrogen takes place according to the overall reaction equation C+H.sub.2 O=CO+H.sub.2 ; a conversion of carbon monoxide into carbon dioxide and hydrogen according to the overall reaction equation CO+H.sub.2 O=CO.sub.2 +H.sub.2 and finally, methanization of carbon monoxide into methane and water according to the overall reaction equation CO+3H.sub.2 =CH.sub.4 +H.sub.2 O. This reaction cycle is endothermic overall. The catalyst not only accelerates the gasification, but also the adjustment of the conversion and methanization equilibrium.
The product gases hydrogen, carbon monoxide, carbon dioxide and methane as well as unreacted water leave the reaction vessel. After the unreacted water is condensed, this gas mixture can be further processed into synthesis gas, hydrogen gas or natural-gas substitute gas.
To generate the steam with a gaseous catalyst which is dissolved homogeneously, steam with a temperature of about 500.degree. to 800.degree. C. and an initial pressure of about 300 bar to 500 bar is produced from a dilute aqueous solution of the catalyst and expanded into the reaction device to the reaction pressure of 60 bar to 140 bar.
If the catalyst-containing steam with the relatively high initial pressure is produced from the aqueous solution of the catalyst in a steam generator, there is the danger of considerable corrosive action of the catalyst on the material of the steam generator. Furthermore piping of the steam generator would quite likely get clogged up because the impurities of the catalyst which are insoluble in steam, deposit on the wall of the pipes in the manner of boiler scale.